Epoxy resins and stable aqueous dispersions thereof

Details Epoxy resins and stable aqueous dispersions thereof Epoxy resins and stable aqueous dispersions thereof

1999-09-07

2001-08-07

Dawson, Robert (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C523S427000

Reexamination Certificate

active

06271287

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to novel epoxy resins and stable aqueous dispersions thereof. Stable aqueous dispersions of epoxy resins are useful in, for example, paper coating and foam backing applications. These dispersions can be used as a crosslinker for other latexes such as S/B latex and carboxylated S/B latex.
Water-borne dispersions of epoxy resins are disclosed, for example, in U.S. Pat. Nos. 5,118,729; 5,344,856; 5,424,340; and 5,602,193, which disclosures are incorporated herein by reference, as well as Japanese Patent Application Kokai: Hei 3-157445.
One of the problems with state-of-the-art water-borne epoxy dispersions is that the shelf-stability of the dispersions is not sufficiently long. It would therefore be an advantage in the art to discover a water-borne epoxy resin with long (greater than 6 months) shelf stability.
SUMMARY OF THE INVENTION
In one aspect, the present invention is a composition comprising a mixture of an epoxy resin and a low temperature nonionic surfactant, a high temperature nonionic surfactant, and an anionic surfactant which, in combination with the low temperature surfactant and the high temperature surfactant, reduces the interfacial tension value of the epoxy resin as compared to the interfacial tension value of the epoxy resin in the absence of the anionic surfactant; wherein the low temperature nonionic surfactant is characterized by having a molecular weight of not less than 1,000 and not more than 7,000, the high temperature nonionic surfactant is characterized by having a molecular weight of greater than 7,000 and not more than 20,000, and at least one of the following criteria is met:
i) the weight-to-weight ratio of the high temperature nonionic surfactant to the anionic surfactant is greater than 3:1;
ii) the weight-to-weight ratio of the sum of the low temperature nonionic surfactant and the high temperature nonionic surfactant to the anionic surfactant is greater than 4.5:1;
iii) the total surfactant concentration is 5 to 20 weight percent, based on the weight of the total surfactants and the epoxy resin.
In a second aspect, the present invention is a composition comprising a stable aqueous dispersion of an epoxy resin stabilized by a low temperature nonionic surfactant, a high temperature nonionic surfactant, and an anionic surfactant which, in combination with the low temperature surfactant and the high temperature surfactant, reduces the interfacial tension value of the epoxy resin as compared to the interfacial tension value of the epoxy resin in the absence of the anionic surfactant; wherein the low temperature nonionic surfactant is characterized by having a molecular weight of not less than 1,000 and not more than 7,000, the high temperature nonionic surfactant is characterized by having a molecular weight of greater than 7,000 and not more than 20,000, and at least one of the following criteria is met:
i) the weight-to-weight ratio of the high temperature nonionic surfactant to the anionic surfactant is greater than 3:1;
ii) the weight-to-weight ratio of the sum of the low temperature nonionic surfactant and the high temperature nonionic surfactant to the anionic surfactant is greater than 4.5:1;
iii) the total surfactant concentration is 5 to 20 weight percent, based on the weight of the total surfactants and the epoxy resin.
In a third aspect, the present invention is a stable aqueous dispersion of an epoxy resin prepared by the steps of:
a) continuously merging into a disperser, and in the presence of an emulsifying and stabilizing amount of a surfactant mixture, a flowing stream of water flowing at a rate r
1
, and a flowing stream containing an epoxy resin flowing at a rate r
2
;
b) mixing the streams with a sufficient amount of shear to form a high internal phase ratio emulsion; and
c) diluting the high internal phase ratio emulsion with water to form the stable aqueous dispersion;
wherein the surfactant mixture includes a low temperature nonionic surfactant and a high temperature nonionic surfactant, wherein the low temperature nonionic surfactant characterized by having a molecular weight of not less than 1,000 and not more than 7,000, the high temperature nonionic surfactant is characterized by having a molecular weight of greater than 7,000 and not more than 20,000; and where r
2
:r
1
is in such a range that the volume average particle size of the dispersion is not greater than 2 microns.
The present invention addresses a problem in the art by providing a water-borne epoxy resin having a shelf stability of greater than 6 months.
DETAILED DESCRIPTION OF THE INVENTION
The surfactant package is critical to the shelf stability of the epoxy dispersion of the present invention. At least two classes of surfactants are used, the first being a low temperature nonionic surfactant, and the second being a high temperature nonionic surfactant. Preferably, a third class is used as a cosurfactant for the low temperature and high temperature nonionic surfactants.
The low temperature nonionic surfactant is characterized by having a molecular weight of not less than 1,000 and not more than 7,000. Preferred low temperature nonionic surfactants are illustrated:
where the sum of n, m, and p in Formula I is such that the molecular weight of Formula I is not less than about 1,000 Daltons, more preferably not less than about 2,000 Daltons, and not more than about 7,000 Daltons, more preferably not more than about 5,000 Daltons. Commercially available Formula I low temperature nonionic surfactants include Hydropalat 3037 nonionic surfactant (available from Henkel, n+m+p=40), Emulgin PRT 100 nonionic surfactant (available from Henkel, n+m+p=100), and Emulpon EL 42 nonionic surfactant (available from Witco, n+m+p=42);
CH
3
(CH
2
)
x
O(CH
2
CH
2
O)
y
—H  Formula II
where x is from about 10 to 18, and where y is from about 30 to 50, more preferably from about 35 to about 45. A commercially available Formula II low temperature nonionic surfactant is Disponil TA 430 nonionic surfactant (available from Henkel, x=C
11
-C
17
, y=40);
where R
1
is oleyl (9-octadecene-yl), and R
2
is either
where the sum of w and z is not less than about 10, more preferably not less than about 15, and not greater than about 30, more preferably not greater than about 25. A commercially available Formula III low temperature nonionic surfactant is Sorbanox AO nonionic surfactant (available from Witco), which is a mixture of the Formula III structures.
The high temperature nonionic surfactant is characterized by having a molecular weight of greater than 7,000 and not more than 20,000. Preferably, the high temperature nonionic surfactant has the following structure:
where each e is not less than about 10, preferably not less than about 15, most preferably not less than about 20, and not greater than about 50, more preferably not greater than 40, and most preferably not greater than 30; and f is not less than about 100, more preferably not less than about 200, and most preferably not less than about 250; and preferably not greater than about 500, more preferably not greater than about 400, and most preferably not greater than about 300. Examples of commercially available high temperature nonionic surfactants include Atsurf 108 surfactant (available from ICI) and Pluronic F108 surfactant (available from BASF Corp.), each with a molecular weight of about 14,000 (e=24; f=255).
Another preferred high temperature nonionic surfactant has the structure of the Formula I nonionic surfactant, wherein the sum of n, m, and p is such that the molecular weight is greater than 7,000 and less than 20,000 Daltons. An example of a commercially available high temperature nonionic surfactant is Emulgin PRT 200 nonionic surfactant (available from Henkel). Other examples of suitable high temperature nonionic surfactants included ethoxylated mono- or dialkyl phenols such as polyethylene glycol nonyl or dinonyl phenyl ethers. An example of a commercially available ethoxyl

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